1. Field of the Invention
The present invention relates to a liquid level detecting device and a processing apparatus using the same, and more particularly, to a liquid level sensing device used in a plasma apparatus, CVD apparatus, sputtering apparatus, ion implantation apparatus, etc.
2. Description of the Related Art
It is ascertained that highly anisotropic etching can be effected by cooling a wafer, for use as a to-be-processed object, in a plasma etching apparatus, for example. The cooling temperature of the wafer tends to be lower.
A very-low-temperature medium, such as liquid nitrogen, must be used to cool the wafer to a lower temperature.
In developing an apparatus in which a cooling jacket for holding liquid nitrogen is arranged adjacent to a susceptor for supporting the wafer, however, it was revealed that control for maintaining a predetermined surface level for the liquid nitrogen in the cooling jacket is very difficult.
Since the liquid nitrogen is a very-low-temperature medium of -196.degree. C., a mechanical liquid level sensor cannot be reliable enough to detect the liquid level satisfactorily by detecting mechanical contact or non-contact with the liquid, due to restrictions in temperature compensation.